Method of particle size grading and product



Sept. 29, 1942. D w 5 2,297,169

METHOD OF PARTICLE SIZE GRADING AND PRODUCT Filed Nov 12, 1941 ATIO 0FSCREEN OPENING |N INCHES TYLER STANDARD SREEN MESH Patented Sept. 29,1942 l'l'E STTES FATE T OFFCE METHOD PARTICLE SIZE GRADING AND PRODUCT14 Claims.

This invention relates to the production of massive bodies from granularmaterial, and consists in a mass whose constituent grains are graded insize according to a formula that I have discovered to afford the optimumresult and in supplementary methods of procedure, whereby a body ofmaximum density may be produced. The invention finds practicalapplication in concrete building and in the production of articles ofceramic ware and refractories.

In the accompanying drawing certain data are plotted, and the plottingwill be referred to in the ensuing description.

It long has been known in the production of bodies from granularmaterial, that, by sizegrading of the particles, increased density ofpiling may be gained. Various formulae to determine grading have beenpublished, but the results have been mediocre. Onesuch formula, based onsize divisions each 1.414 coarser than the next finer, shows a ratio of1.20 for the amount on each screen as cdmpared with the next finer(0.8333 for amount on each screen as compared to the next coarser). Inconcrete building, particularly, the common practice is to accept anduse the Portland cement content of the mixture in the condition ofgranulation that the producer has given to it in placing it on themarket, and in such quantity as the concrete mixture requires. This isdone in ignorance of the fact that, by bringing the whole of thegranular constitutents of the mass (cement included) into conformity toa formula of size grading, superior results are to be attained. In priorpractice, furthermore, there has been no recognition of the fact thatsize grading should, to achieve best results, be carried into the veryfine and powder-like portion of the whole-into the portion that willpass through a 325-mesh screen.

To achieve maximum density, the grading should be such that the largerparticles stand apart; that, on the average, every particle, tangentnecessarily to a larger particle (in this detail the largest particlesonly are excepted), should be supported elsewhere by particles ofsmaller size. In a mass so graded, the particles are, geometrically, inan assembly of maximum mechanical instability; and, consequently, inaddition to the desired characteristic of maximum density, the so gradedmass is (when in slip condition) in a state of maximum fluidity. Thisfurther characteristic of maximum fiuidity is of peculiar value in thearts of concrete work, ceramics, and refractories, since but a minimumamount of liquid is required to form the mass into a paste or slip thatmay be shaped or molded as desired.

I have discovered a formula that, being followed, will afiord in highestdegree the characteristics indicated, and as a correlative of ,suchformula I have developed an average cumulative plot upon a coordinatechart, as illustrated in the accompanying drawing, indicative of agraded granular mass that is of maximum density, that possesses maximumfiowability, that requires a minimum quantity of water to bring itto thecondition of a workable paste, that affords a shaped body of minimumdrying shrinkage, a dried body of minimum porosity, and good continuityin the substance of the fired ware.

I found that the percentages on successive screens could be accuratelymeasured to 200- mesh. On finally arriving'at my general formula itbecame evident that fully as accurate grading is required of the finersizes as is required for that coarser than ZOO-mesh. This last fact wasproven by including from two to six groups of known particle sizessmaller than 325-mesh. Further, I found that, the closer the fractionscoarser than ZOO-mesh approached my average curve, with minus ZOO-meshfractions at a minimum, the closer the mixture approached fiowability,but that satisfactory flowability does not occur unless there bematerial present of smaller particle size than that which remains one325-mesh screen, such material of smaller particle size also being 7preferably graded.

in which S=cumulative volume per cent of any number (n) of fractionsthat, passing through 0.185-inch openings (4-mesh screen). are arrestedon succeeding smaller-meshed screens of tion=0.96. Thus I havediscovered that my specific cumulative volume per cent plot matchesthegeneral mathematical equation y:m in which represents the size(expressed as a function of largest particle size) of screen-mesh and ythe percentage (expressed decimally) that passes the screen. It matches,not only in the portion coarser than 200-mesh, but also down to0.000008-inch size (approximate average size of individual clayparticles) which is the smallest size for which comparisons were made. Ithus have three points of the specific curve that fit the y:a: curve; atmaximum size (point A on the curve), at 200 mesh (point B), andat0,000008-inch diameter (point C). :m is hence the general equationsought. It is general for any maximum size. Its form has the physicalsignificance that, if the smallest size were infinitely small, the dryporosity of a formed dried mass of such a gradation would be zero, nomatter what the size of the maximum particle. This fact may be set forthas follows: This is a particle-size gradation, hence the particles arein contact with one another. Since a uniform law is followed frommaximum size'to infinitely small size, there can be no size at which theparticles are in different arrangement than at any other size, hence theparticles must be uniformly in contact at all sizes. Since the particlesare uniformly in contact at all sizes and the smallest is infinitelysmall, the interstitial space is infinitely small. Geometrically, such amixture has maximum mechanical instability, and hence exhibits (when inslip form) maximum 'flowability. Further, the respective volumes ofmaterial and numbers of particles of the various sizes geometricallyinsure that size gradation is uniform throughout any fluidized masshaving this gradation.

In plotting the :19 equation I lay out the values of x from 0 to 1algebraically (non-logarithmically) along ten successive logarithmiccycles, on the one-way logarithmic chart, and the values of y from 0 to1 are ranged uniformly along the non-logarithmic ordinate of the chart.In plotting the curve or graph of the equation. the following values ofa: and y are used:

' I also lay out on the abscissa the ratio of the particle diameter d ofeach fraction of the material to the diameter D of the largestparticles,

the values of such ratio beingdistributed logarithmically. The largestparticle diameter in this case is 0.1850", which equals the size of themesh opening of the No. 4 screen of the Tyler screen series. Thus, thevalue of the ratio d/D for the largest particle or mesh size is etc.Since the largest particle diameter D has unit value (a value of 1), andsince 1 on the z axis or abscissa of the chart equals 10 cycles of thelogarithmic scale, any value of a: may be computed in accordance withthe equation:

:i::1+0.1 (log. d/D) Thus, the value of :1: for the largest particlesize or screen:

The value of a: for the next smaller particle or screen size:

' 0.1310 1+0 .1(log =1 +0.1(log .71 =1 +0.1 1.851) =1 +0.1(9.851 10) =1.+.9851 l .9851

The value of a: for the next smaller particle or screen size:

And so it is with each value of x, it being noted that each of suchvalues of a: is a function of the ratio of a particular particle or meshsize to the largest particle or mesh size, and is not limited to anygiven system of screen sizes.

Each value of y is, of course, equal to the cube of a particular valueof 2. That is, when 1:1, 11:1; when :c:.985, 1:.955; when :1:=.9'l0.'y:.913; etc., the values of y being the decimal equivalents ofpercentages.

In applying my formula (-'-S:y:cumulative. volume per cent finer thanany given size) to. the y=x equation, I reduce the percentages expressedin the formula to decimals, that is, to the same sort of units as a: andy in the ZI=$3 equation are expressed. Thus, for the Tyler system ofscreen sizes In computing in accordance with the formula for thefraction having the. particles of largest size (the 4 mesh Tylerscreen), the value of n is 0 and the formula reads:

10.4698 (0)=1 (Note point A on the graph.)

In the case of the 200 mesh screen, where -n=12, the formula reads:

log .96 1.98227= 9.98227- log .96X12=l19.78724120= 1.78724, the numberof which: .6127

1.815=.1 8i (Note point C on the graph.)

Thus, it will be seen that my formula, 100S= cumulative volume per cent(expressed decimally in this case), matches the y=ac curve, and, havingestablished this, it will be understood the y=zr equation may be used asthe controlling factor in size-grading of materials whose maximumparticle size is 0.1850". What particular series of screens is in factused does not signify, since the value of a: for any particular screensmaller than the maximum mesh size of 0.1850" is a definite function ofthe ratio of the particular screen size to the largest size; that is,a:=1+0.1 (log d/D).

In case the material to be size graded has a maximum particle size of0.328" (20 mesh by the Tyler series) the same y=x curve is employed, butthe 20 mesh screen is given unit value (as was the 4 mesh screen above)then the values of the ratio of d/D are computed relatively .to size ofopening of such 20 mesh screen, and the values of a: for the successivescreens are determined in accordance with the equation x=1+0.1 (log(II/D). And so the equation 11 .79 is adaptable to the size-grading ofvarious materials, whatever be the maximum particle size;

To check that other size gradations do not yield the y=at equation, andhence cannot yield the desired results, for which it is the exact,equation, I assumed other values of r at size 0.000008 inch (seeaccompanying cumulative plot) and, by inserting these in the equationT-r calculated the corresponding valuesof a. Using these assumed valuesof r and the corresponding derived values of a in the equation for 200mesh, I found that I had a My curve shows that 18.5 cumulative volumepercent of a gradation, whose maximum size is 0.185 inch, should be finerthan average clay grain size (note point C). It is known that theultimate clay grain size of refractory clays is commonly of one order.Further, I have found that, using nothing of finer grain size than clay,in preparing masses according to my formulae,

the resulting formed dried mass, made of grains of near zero porosity,has had porosities of near 18.0 per cent. I thus find that the inclusionof suitable percentages of suitably graded sizes of smaller than0.000008-inch diameter has effect in decrease in the porosity of theformed dried mass. The ratio of average clay grain size to maximum grainsize is which expressed as a fraction:

the crusting" during drying of clay containingsuitable amounts of sodiumsilicate. As drying proceeds, colloidal silica collects near the surfaceof the clay, with resultant formation of a nonporous layer that retardsfurther drying of the interior of the mass.

Formulae previously devised for the grading of granular masses have beenempirical and have not been based on knowledge of what are the bestconditions in any given case. On the other hand, y=m defines the limits.Thus, my above formulae produce good flowability, low water content, lowdrying shrinkage, and low dry porosity, and otherwise improve the formedmass, to such a degree as to result in greatly improved behavior ofmasses graded in accordance therewith during the various processingsteps, and in greatly improved quality of the finished ware, and,specifically, in improved continuity of the structure of the fired ware(absence of voids formed by shrinkage) Tests, consisting of grading ofthe portion finer than 32'5-mesh, have resulted in checking the aboveformulae which, as far as I am aware, are different from previousformulae, even in the portion coarser than 325-mesh. The grain sizes inthe portions finer than 325-mesh may be determined by elutriation,micro-examination, ultra-centrifuge, ultra-filtration, and by settlingtests. In practice, approach to satisfactory grading is indicated byease of fiow of the wetted mass, low amount of Water required to causeflowing, low porosity of the dried mass after flowing, and (in a ceramicmass) by good continuity in the substance of the fired mass.

I have discovered that, except for surface phenomena, such gradationsflow readily. Most of the total particle surface consists of the surfaceof the particles finer than 325-mesh. Primarily interest accordinglycenters in surface effects of the portion finer than 325-mesh (50.4%according to my formula for-4-mesh maximum size) and more particularlyin the portion finer than 0.203 micron (18.5% according to saidformula).

In certain cases granular material of other gradation values may, bycareful preparation, be made to assume a condition of low voids, but thematerial does not in these cases readily assume such arrangement, anddoes not afford such continuity of the substance of the fired ceramicware as is gained in following my invention. On the other hand,gradations made according to my formulae automatically assume sucharrangement, without resort to any tamping or arrangement process. Forinstance, slip-cast wares made by my formulae are uniform throughout asto the distribution of the graded particles. This is, possibly, becauseof the fact that, for a given weight, the number of spherical particlesincreases inversely as the cube of their diameter. That is, a sphere ofa given diameter has a weight equal to that of eight spheres of halfthat diameter; the result of this being that there are not enoughparticles of near any one diameter to permit of their coming intocontact,. to cause bridging. Such automatic assumption of particlearrangement is useful in pouring of concrete.

It is possible that in certain masses comprising graded grains, theportion of the mass smaller than a certain grain size does not, inmanufacture and in use, shrink much more than does the coarser material.In such case I may prefer to grade according to my formula theflnergrained portion of the whole, up to a given maximum grain size, andto fill more or less completely this graded portion with coarser-grainedmaterial. For best results these coarser particles should not be sogreat aproportion of the total massthat they would make contact one uponanother, and thus bridge, and cause discontinuity in the mass. Adry-press raw flint-clay body may be such'a mass, as are most masses ofconcrete. I may prefer to grind a very fine portion of such a ceramicbody, and to mix this with coarser sizes, graded per my formulae, tofluidize the mass with proper agents, and then to use this mass forsuitably wetting the coarser-grained raw flint and bringing it to aconsistency suitable for dry pressing. I may prefer to use from 60 to90% by weight of the coarser material.

I have found that wetted masses of certain fine-grained ceramicmaterials tend to assume a mild set, suflicient to prevent free flowingof the mass. Free flowing is especially necessary in the molding ofintricate shapes. My tests indicate that materials that behave in thismanner are of near one grain size, and that their grains tend to orientthemselves one to another. Such orientation may possibly be caused byforces residing on or in the individual grains, or by some other cause.I have found, however, that if the grains are suitably graded in sizeaccording to my formulae, flowing is frequently not appreciablyretarded.

An example of one way of obtaining a gradation in accordance with myformulae follows:

It is common knowledge that, on the crushing of homogeneous materials bythe usual methods, such as jaw crushers, rolls, dry pans, and similarmethods, the majority of the crushed particles form a hump" in the curveindicative of quantity coordinated with particle size, within a sizerange of approximately 2.5 diameters with the balance of the materialextending largely in a smooth rapidly decreasing gradation to smallersizes.

I find that, if I start with homogeneous material, that is relativelyhard and tough and of approximately two-mesh size, and grind it in themanner outlined below to approximately fourmesh size, the resultantproduct is of smooth gradation, the majority of which extends over asize range of approximately eight diameters, with the balance of thematerial extending, largely,

in a smooth, rapidly decreasing gradation to smaller sizes.

The method of obtaining such smooth gradatlon consists in grinding in aball mill containing grinding media of suflicient maximum size to insureready breaking of the maximum-sized particle of the infed material,together with sufficient water to cause the particles of infed materialto adhere to the grinding media, but not to pack. With the maximum-sizedgrinding media are associated assorted smaller-sized grinding media, butstill of such size that they are not crushed by the larger-sizedgrinding media. For instance, flint pebbles in a silica-lined ball millmay be used, in which the pebbles range from approximately five-inchdiameter to approximately two-inch diameter. In case a continuous millis used, the material, when ground to the desired degree, is forced fromthe mill by incoming material. If need be, the desired degree ofgrinding may be attained by passing the material from a first mill toone or more additional mills.

A second stage in the fineness of grind, composed of particles, themajority of which will spread in a smooth gradation over approximatelyeight additional diameters, can be prepared by using material that hasalready been ground to approximately twenty mesh, either by ordinarycrushing or by the above method of wet grinding, and grinding as above,except that the maximum-sized grinding media are just suflicient todisintegrate the twenty-mesh particles of material. For instance, ifflint pebbles are used, the

maximum-sized pebble may be approximately smallest size of the constantcurve portion of the grind la'st described above.

Suitable combinations or grinds of the three stages described aboveyield close approximations to my formulae. A further aid in smoothingout "humps" in the curve indicative of gradation in this three-stageprocedure is to grind said suitable combination for a short period oftime with grinding media of intermediate size. A further aid in theproduction of suitable size gradations from clay grogs is thepreparation of suitable gradations of unfired clays, slight bonding ofthese graded grains into dobies, and calcining of the dobies. Suchcalcined material readily crushes to the original gradation. To insurethat the calcine will disintegrate readily, I may prefer to incorporatematerials with the clay, such as quartz and kyanite, that expand tofriable masses on being flred. 'Ifhis serves to produce the groundmaterial with a minimum of grinding efiort and with a minimum ofcontamination from the grinding media. Flint clay is responsive to thistreatment.

Production of the finer sizes of such size graca tions is aided bygrinding together fine-grained materials of different degrees ofresistance to abrasion. Instances of this are the grinding together ofraw kyanite, heat-softened kyanite, and heat-expanded kyanite; again,raw quartz with heat-expanded silica; and, again, silica or kyanite withclay and diaspore raw or calcined. Although coarse sizes may besimilarly benefited, this method is particularly useful in connectionwith minus 325-mesh particles, as there is apparently no other method ofgrinding available (on account of insuflicient area of grinding, media)for rapid production of minus 400-mesh sizes, without reducingpractically .all of the particles of the mass to these small sizes, thuspreventing attainment of the desired size gradation. This method alsoavoids introduction of excess impurities during such size reduction.

Usual good practice as to mill charge of grinding media and material tobe ground applies to this type of grinding. I have found that, if onlythe particles of the infed material be small enough to be disintegratedby the maximumsized pebbles used as grinding media, the smaller theaverage pebble-size the finer is the grind that can be produced.

A certain range of colloidal sizes can be at tained in the grinding ofraw clay; preferably by grinding the clay to some extent as above. Ifraw clay be ground together' with harder material, th particles of theharder material will serve in part as grinding media for the clay, whilebeing themselves ground.

Another range of colloidal sizes is attained by the partial hydrolysisof the infed material, occasioned by fine grinding in contact withwater. For instance, some colloidal material is produced on the finegrinding of silica, alumina, and the aluminum silicates. In fact, silicaand alumina, wet-ground together for suflicient time, produce somehydrous aluminum silicate.

Other means of producing partial hydrolysis are found in the use ofmeans and materials that to some extent attack the particles of theinfed material. For instance, on grinding silica and alumina togetherunder elevated steam pressures, hydrous aluminum silicate is the stablephase, and some of it is formed. Furthermore, I find that the treatingef silica, alumina, and aluminosilicates with gaseous fluorine or agaseous fluorine compound such as hydrofluoric and hydrofiuo-silicicacid gas and of other fluorine compounds such as ammonium fluoride orammonium bifluoride effects to a degree decomposition of the particlesurfaces. Such surface decomposition commonly results in the hydrolysisof one or more of the reaction products, and in the production of somecolloidal material. I find that such reactions are aided by being conducted in conjunction with and during a grinding operation. I may preferto grind the batch for a time in the presence of these materials, eitherdry or wet, and at room temperature or at elevated temperatures. In thecase of alumina-silicate reactions, removal of either silica or aluminafrom the reaction allows the decomposition of the sistant to abrasionthan is the unfired kyanite.

My invention lies further in the discovery that a graded mass ofgranular material, preferably graded according to the formula givenabove,

' may be yet more closely consolidated,-and its density yet more greatlyincreased, by subjecting it to further particular treatment.

It is common knowledgethat, in clays, exchangeable bases take updefinite positions in the crystal lattice of the ultimate clayparticles; that in clay suspensions in water, and other suspendingmedia, such exchangeable cations serve as the connections between clayparticles; and that, in cases in which such cations bring aboutcoagulation of clay particles, it tends to be an oriented coagulation.Further, it is known that clay particles in such' suspensions can beoriented by passing electric current through the suspensions and bysubjecting the suspensions to electric fields.

Reasoning from the above and other known chemical facts, I haveconcluded that such sus pended .ultimate clay particles, and similarsuspensions r' many other kinds of particles, carry, or are capable ofcarrying, electrical charges. By altering the direction of an "electriccurrent that I may cause to pass through such a suspension, or byaltering the direction of lines of force of an electric field to which Imay subject such a suspension, it is possible to break down givenorientations and form still other orientations in conformity with thealtered directions. Still further, since the ultimate particles of sucha suspension can carry electric charges, it is possible to orient andalter the positions of the particles relative to each other bysubjecting the suspension to any electric, electronic, magnetic field,electro-magnetic induction, or positive or negative ray forces ofsuflicient magnitude. Similarly, by more or less continuously alteringthe direction of such-a force, it is possible to keep the ultimateparticles in more or less continuous movement relative to one another.By using such forces of sufiicient intensity andby varying the intensityI am able to gain maximum and desirable time of disorientation ofultimate particles and produce other desirable effects.

Multiple forces of the nature specified may be simultaneously applied;they may be applied in I parallel directions or at angles to oneanother, in the same plane or in different planes, and in changingdirections relative to one another. Conventional means may be employedthat the dispersions may be penetrated by direct or alternating current,or may be brought within and made subject to magnetic fields, toelectro-magnetic induction, or to positive or negative rays. The wavesof force may vary, not in direction only, but in intensity as well. Incase direct or alternating current is used directly for this purpose, Iprefer to use a current of between 22 and 1500 vlolts, and, withamperage suitably small, the current becomes relatively safe to handle.

7 A specific means of accomplishing above rapid change of orientation isto place a mass of the material within an annular coil, so wound thatthe particles within th mass of material will be rapidly oriented andtheir orientation altered when an alternating current is passed throughthe coil. The field intensity is, of course, sulficient to causeorientation.

In concrete and in ceramic masses containing granular and'colloidalmaterial. I may' prefer to cause movement of particles relative to oneanother, by causing at least some of the particles to vibrate by meansof passing high-voltage highfrequency electric current throughpiezo-electric crystals. the piezo-electric materials being situatedeither outside of or within the mass being acted upon. I may prefer touse Rochelle salt. quartz, mullite, particles that are largely alumina,magnesium chloride, ammonium chloride, magnesium ammonium chloride,ammonium fluoride, ammonium fiuo-silicate, and other materials,including constituents of the ceramic mass, as the piezo-electricmaterial, and vary the frequency and voltage to suit the material used.I may prefer so to act on ceramic masses while they are under pressure.Crystalline constituents of ceramic masses frequently contain crystalstrain, particularly in fired particles. I may vibrate a dispersion bymeans of piezo-electric vibration of these strained particles.

Piezo-electric excitation may be set up by causing particles of quartzpresent in a dispersion to vibrate. Particles of quartz are normallypresent in a concrete mix and in a ceramic casting slip also.

Piezo-electric excitation is commonly carried out by passing theexciting force through the crystal in a given direction. I may prefer toorient piezo-electric crystals in a mass of particles, such as concrete,ceramic materials, and refractory materials by the methods hereof; and,while so oriented, to pass a piezo-electric exciting force through suchcrystals in the most favorable direction. For instance, I may prefer soto orient particles of quartz, kyam'te, clay, magnesite, chrome, andauxiliary piezo-electric materials, including organic piezoelectricmaterials, and to subject them to piezo-electric exciting force while sooriented.

In case the two sets of forces interfere, I may prefer to apply themalternately to the piezoelectric particles. In case alternatingelectrical forces are used for this purpose, I may choose to synchronizethese forces, so that one is acting with minimum effect on the particleswhile the other is acting with maximum effect. For instance, one forcemight be one fourth of a cycle behind the other.

I may prefer to use this piezo-electric crystal vibration method in theforming of concrete masses and of ceramic masses containing minimumwater contents, whether the ceramic mass be shaped by slip casting, bypressing, or by other forming method.

By subjecting the particles of the suspension to such orienting andpiezo-electric influences rigidity of a mass may be diminished, facilityof flow increased, and other good purposes served.

One specific practical application of the invention is found indecreasing the rigidity of watercontaining masses of concrete, so thatthey can be flowed to position and form a relatively voidfree finishedproduct. Another application is found in doing the like in the case of aceramic mass, so that the mass, containing an amount of water less thanotherwise is practicable, may still be flowed into a mold, or otherwiseshaped. I find a result of disorientation of particles in ceramic andother masses to be low porosity of the formed dried masses.

In particular cases I prefer to keep the particles disoriented only longenough to permit forming (as in a mold) the masses containing them. Theparticles may then be re-oriented, for the purpose of giving to themolded material a set, so that the molded article can be removed fromthe mold within a minimum period of time, and so that other usefulpurposes can be served. The molding may be performed by slip casting,pressing, or by other suitable means.

Referring again to the crystal structure of clay particles, it iscommonly known that the molecules of polar liquids, such as water,attach themselves to the ultimate particles of suspensions in definitelyoriented positions with reference to the cation bonds between theparticles. Reasoning from this and other known chemical facts, suchwater isf'I believe, little attached to and hence more easily removedfrom disoriented particles than from oriented material. I, therefore,prefer to alter the orientation of ultimate particles and to disorientthem during at least part of the time of the drying of masses containingthem. Such treatment serves to permit easier removal of water from themasses.

In ceramic masses, such control of orientation of ultimate particles hasthe advantage that it permits of wider variety in the applications of anumber of ceramic materials. Specifically, it permits the use of certainclays in slip-cast ware that give unusual strength to the ware, andwhose particle-size range apparently is unusually great.

I may in particular cases and with good effect disorient the silicaparticles of silica jellies.

I have described how I size grade according to formula the particles ofcements, concrete, and ceramic casting slips to achieve a minimum ofvoids; how this grading insures automatic arrangement with minimumvoids, and howboth by such grading and by methods of polarization andpiezo-electric vibration I am enabled to use a minimum of water in theshaping of such masses. The combined result of all these in ceramic wareis a dry porosity of ware which, to my knowledge and belief, is lowerthan has heretofore been achieved, either by slip casting or by anyother method. Size grading according to my formulae has the furtheradvantage in ceramic ware that, with lack of bridging between particles,the raw ware is more rubbery, and, hence, more resistant to injury bythermal shock. I have found this to be a feature particularly valuablein the case of raw wares of high thermal expansion, such as those highin quartz.

This method of particle-size gradation and fiuidizing will be found tobe of great utility in the making and placing of concrete. First, in themanufacture of cement, the strength and covering power of the cement canbe improved by extending according to my formula the lower limits ofparticle size. Next, intermediate sizes of aggregate, sand, and finesand can be used in compliance with my formula to augment and completepresent-day gradations. Suitable colloidal material of yet finer sizesthan the cement can be introduced according to the'formula, to

fill the interstices between the cement particles.

and the cement can be of such composition that it will liberate asuitable amount of such suitable colloidal material. Such grading ofconcrete yields a mixture that has a new order of flowability. Also,since concrete commonly contains quartz particles, that can bepiezo-electrically excited, such excitation canbe utilized to furtherfiuidize them.

In the practice of my invention I have produced superior refractoryblocks for glass tanks or furnaces. Slip-cast refractory blocks made inaccordance with the invention have a more continuous and superiorstructure.

In accordance with the teachings of the invention' better concrete maybe obtained with a smaller proportion of cement, the most expensiveingredient of the concrete mix. Specifically, it appears possible toproduce better concrete (than is now used in concrete construction) withmixes that include from 15 to 21 per centpcement, which is from A; toless cement than is used in the usual mixes.

7 particles of less than 0.000008 of an inch The application for theseLetters Patent consisted in a continuation in part of application SerialNo. 239,184, filed November 5, 1938. And notice is hereby given of myapplication Serial No. 285,961, filed July 22, 1939, comprising adivision of the first filed case.

I claim as my invention:

1. A body of finely divided material of varied and graded particle sizeand of maximum density, formed of a plurality of grades compoundedaccording to the formula y=x in which y=the part of the whole that willpass through any given screen having segregating action and effectupon'the body, and a=the size of the mesh of that screen, expressed as afunction of the ratio of such mesh size to the largest particle size ofthe material.

2. A dense mass of size-graded particles in which the particles aregraded according to the equation y=zr in which i v particular particlesize 'maximum particle size) and y is the proportionate part of thewhole that is of such particular particle size and smaller.

3. A dense mass of size-graded particles, including small particlesthat; will pass through a 325-mesh screen, such small particles being ofvarious particle size, graded according to the equation z/=.r in whichparticular particle size 'r n aximum particle size) and y is theproportionate part of the whole that is of such particular particle sizeand smaller.

4. A dense mass of size-graded particles, including particles of adiameter less than 0.000008 of an inch, the particles of such smalldiameters being graded according to the equation Far in which particularparticle size 'maximurn particle size) and y is the proportionate partof the whole that is of such particular particle size and smaller.

5. A dense mass of size-graded particles in which the particles aregraded according to the equation y=x in which particular particle size Q'maximum particle size) and y is the proportionate part of the wholethat is of such particular particle size and smaller, said massincluding substantially 18.5 per cent of in diameter.

I 8. A ceramic slip of size-graded particles in which the particles aregraded in accordance with 6. A dense mass of size-graded particlesineluding particles of graded size, from a diameter '7. A dense mass ofsize-graded particles in which a matrix of finer particles graded inaccordance with the equation y=x (in which particular particle size) x'maximum particle size and y is the proportionate part of the whole thatis of such particular particle size and smaller) contains ,from 60 to 95per cent of coarserparticles.

the equation y=a: in which particular particle size 1 'maximum particlesize and y is the proportionate part of the whole that is of suchparticular particle size and smaller.

9. A dense mass of size-graded particles in which the particles aregraded according to the equation 11:09, in which g particular particlesize) maximum particle size and y is the proportionate part of the wholethat is of such particular particle size and smaller,

said mass including substantially 18.5 per cent.

of particles whose diameters are less than ofthe diameter of the largestparticle size.

10. The method of forming particle size gradations that comprisesgrading fines according to the formula y=x in which y=the part of thewhole that will pass through any given screen having segregating action,and .r=the size of the mesh that screen expressed as a function of theratio of such mesh size to the largest particle size of the fines, andcompounding the so-graded fines with a body of coarser particles in suchproportion that the coarser particles stand substantially free fromcontact with each other in the body of the fines.

11. The method herein described that comprises compounding a body ofunfired clay particles according to the formula y=w in which y=the partof the whole that will pass through any given screen having segregatingaction, and ar=the size of mesh of that screen expressed as a functionof the ratio of such mesh size to the largest particle size, bonding theso-graded particles into dobies, calcining the dobies, and then crushingthe dobies and returning the mass to substantially its originalsize-graded condition.

12. The method herein described which consists in grinding in common aplurality of solid particulate materials of different degrees oftoughness, and compounding the particles of the ground mass according tothe formula glen, in which y=the part of the whole that will passthrough any given screen having segregating action, and zc=the size ofmesh of that screen.

expressed as a function of the ratio of such mesh size to the largestparticle size.

13. The method of preparing the finer or colloidal grains of aparticulate material that is size graded according to the formula 11:15,in which y=the part of the whole that will pass through any given screenhaving segregating action, and z=the size of msh of that screenexpressed as a function of the ratio of such mesh size to the largestparticle size, which method consists in chemically decomposing thesurfaces of the coarser particles of the material.

14. The method of preparing the finer or colloidal grains of aparticulate material that is size graded according to the formula :19,in which y=the part of the whole that will pass through any given screenhaving segregating action, and zr=the size of mesh of that screenexpressed as a function of the ratio of such mesh size to the largestparticle size, which method consists in chemically decomposing thesurfaces of the coarser particles of the material while agitating thematerial and causing such particles to rub against each other.

DONALD W. ROSS.-

